Enzymes involved in phthalate degradation in sulphate-reducing bacteria

The complete degradation of the xenobiotic and environmentally harmful phthalate esters is initiated by hydrolysis to alcohols and o-phthalate (phthalate) by esterases. While further catabolism of phthalate has been studied in aerobic and denitrifying microorganisms, the degradation in obligately anaerobic bacteria has remained obscure. Here, we demonstrate a previously overseen growth of the d-proteobacterium Desulfosarcina cetonica with phthalate/sulphate as only carbon and energy sources. Differential proteome and CoA ester pool analyses together with in vitro enzyme assays identified the genes, enzymes and metabolites involved in phthalate uptake and degradation in D. cetonica. Phthalate is initially activated to the shortlived phthaloyl-CoA by an ATP-dependent phthalate CoA ligase (PCL) followed by decarboxylation to the central intermediate benzoyl-CoA by an UbiD-like phthaloyl-CoA decarboxylase (PCD) containing a prenylated flavin cofactor. Genome/metagenome analyses predicted phthalate degradation capacity also in the sulphate-reducing Desulfobacula toluolica, strain NaphS2, and other d-proteobacteria. Our results suggest that phthalate degradation proceeds in all anaerobic bacteria via the labile phthaloyl-CoA that is captured and decarboxylated by highly abundant PCDs. In contrast, two alternative strategies have been established for the formation of phthaloyl-CoA, the possibly most unstable CoA ester in biology.